This invention relates to locked joints for male and female socket pipes with an annular elastomeric gasket being placed in between, and to a gasket for telescopic locked joints in which the male end of one of the pipes penetrates into the socket of the other pipe while at the same time compressing the gasket radially.
When a seal is made, axial movements of one pipe relative to the other which may occur subsequently should be prevented. Indeed, such movements are likely to weaken the satisfactory leaktightness of the joint or even to completely disconnect the initially joined pipes. This problem becomes particularly critical in the case of ducts transporting pressurized fluids; the pressure of the fluid generates substantial forces which tend to separate the elements forming the joint.
Gaskets are known into which regularly distributed locking elements, situated in the front part of the gasket on the open side of the socket, are inserted. In French patent No. 1,490,680, for example, the locking elements, consisting of metal inserts, may rotate by sliding against the inner surface of the socket. The locking elements function by being braced at one of their extremities against an inner face of the socket and, at their opposite extremity, against the outer surface of the male end into which they penetrate with their bevelled profile.
Depending on the manufacturing tolerances of the male end and he point of a metal insert relative to the outer surface of the male end into which it penetrates may vary. In order to obtain an optimum locking, this angle must be situated between certain limits which depend on the desired strength of locking, on the material of the pipes to be connected and on the surface finish of the pipes. If the angle made by the insert with the outer surface of the male end is too small, the locking insert merely rubs against the male end without ensuring actual locking. If the angle is too great, the component of the bracing force parallel to the male end becomes too small to ensure effective locking.
Experience has shown that the metal locking inserts sometimes tend to continue their penetration into the outer surface of the male end during backward or withdrawal movements of the male end relative to the socket. This results in an artificial reduction in the length of the inserts, which promotes their tilting beyond the limits of inclination which must be maintained, and reduces the bracing effect. This furthermore gives rise to a deterioration of the male end which may become as serious as it being pierced or its inner coating coming apart.